In recent years, engines in which a variable valve timing device configured to control valve timings of an intake valve and an exhaust valve in correspondence to a driving state of an engine is mounted for high output, low-fuel consumption and low exhaust gas have been increasingly used. In this type of engines, an engine has been known in which a hydraulic pressure to the variable valve timing device is controlled with an oil control valve unit provided between a cylinder head and a radiator (for example, refer to Patent Document 1). The oil controlled by the oil control valve unit is supplied to an advance chamber and a retard chamber of the variable valve timing device, and a rotation phase of a camshaft relative to a crankshaft is changed, so that the valve timing is adjusted.
Patent Document 1: Japanese Patent No. 5345448B
However, according to Patent Document 1, since the oil control valve unit is mounted in the vicinity of the radiator (heat exchanger), operation characteristics of the oil control valve unit are susceptible to heat from the radiator. Also, in case of a general engine, a transmission cover bulges from a side surface of the engine. When the air flow is hindered at the rear of the oil control valve unit due to the transmission cover, the air is difficult to go through at the rear of the oil control valve unit and the heat is retained, so that it is not possible to effectively cool the oil control valve unit.